The present invention is in a process for the simultaneous removal of nitrogen oxides and sulfur dioxide from an oxygen-containing exhaust gas.
The exhaust gases produced by the combustion of fuel with atmospheric oxygen contain nitrogen oxides as well as SO.sub.2. Both substances are pollutants to the environment and therefore must be removed from the exhaust gases before its discharge to the atmosphere. Typically, such exhaust gases contain between 500 and 10,000 mg/sm.sup.3 SO.sub.2 and between about 100 and 2,000 mg/sm.sup.3 nitrogen oxide, calculated as NO. In addition to SO.sub.2 and nitrogen oxides, the exhaust gases contain nitrogen, water vapor and CO.sub.2 as well as residual oxygen, the latter usually being present in the exhaust gas in a concentration of from 1 to 10%.
In known processes, nitrogen oxides and SO.sub.2 can jointly be removed from the exhaust gases by means of an absorbent solution which contains, inter alia, calcium hydroxide, Fe.sup.2+ ions and ethylenediamineotetraacetic acid. However, such processes involve a considerable structural expenditure and result in solid and liquid residues, which must be after-treated because they cannot readily be disposed of in a dump or discharged into a sewer.
Thus, it is an object of the invention to provide a reliable process which results in a substantially complete removal of SO.sub.2 and of nitrogen oxides from exhaust gases, which can be continuously carried out for an extended period and which results in process products friendly to the environment.